1. Field of the Invention
The present invention relates to a thermoelectric semiconductor and an electronic panel using a plurality of p-type and n-type thermoelectric semiconductors.
2. Description of the Prior Art
Recently, electronic devices such as electronic refrigeration, heating and thermoelectric power generation devices which utilize a Peltier effect and/or a Seeback effect have been in high demand for various uses, such as for the inhibition of freon due to the global atmospheric problem, the local refrigeration for electronic apparatuses, as small refrigerators used for dehumidification, and for the utilization of the waste heat and the like.
In a conventional electronic refrigeration panel, p-type and n-type semiconductor elements each made of a Bi-Te system single or polycrystalline solid material are arranged alternatively in a two-dimensional configuration and electrically connected in series using Cu plates as electrodes.
In a conventional thermoelectric device, polycrystalline sintered materials such as Fe.sub.2 Si or the like is used and p-type and n-type semiconductor elements are jointed with each other directly.
It has been known that the heat absorption amount in respect to the consumed power at the refrigerating side of an electronic refrigeration panel is determined by the performance factor of the semiconductive material used and that the performance factor is represented by Z=S.sup.2. .sigma./k using a Seebeck coefficient S, an electrical conductivity o and thermal conductivity k of the semiconductive material. As is apparent from the above equation, the semiconductive material therefor is preferably required to have a large Seebeck coefficient, a high electric conductivity .sigma. and a low thermal conductivity K. Further, a refrigerator of this type, is driven intermittently after reaching a predetermined refrigeration temperature. In such a case, it is required to have a high adiabatic property at the time when no voltage is applied thereto. In a thermoelectric power generation device, each semiconductor element is required to have a low thermal conductivity in order to maintain a temperature difference between the higher and lower temperature sides.
Further, in a semiconductive material such as Bi-Te system material, there have been proposed various techniques such that Sb and/or Se are added thereto to reduce the lattice vibration in a heat conduction and a polycrystalline solidified body with a controlled grain size is made without growing the single crystal from a molten state to lower the thermal conductivity thereof.
In an electronic refrigeration device, it is said that it is theoretically possible to obtain a temperature difference of about 60.degree. C. between the higher and lower temperature sides in a Bi-Te system semiconductive material, but this generates problems, in that the lowest achievable temperature, at the lower temperature side, becomes higher due to an increase of the temperature at the higher temperature side, if the amount of heat radiation thereat is small. The thermal resistance between an ordinal radiation plate and an ambient atmosphere is about 0.0002 to 0.0005 W/cm.sup.2. deg under a spontaneous cooling and about 0.0004 to 0.0002 W/cm.sup.2. deg under a forcible air cooling and, accordingly, a temperature rise at the radiation side (higher temperature side) is a serious problem.
To solve this problem, in a conventional refrigeration panel, a plurality of p-type and n-type semiconductor elements are arranged alternatively in a rectangular configuration, but with a gap therebetween to give a cross section two or three times as large as the sum of their cross sections obtained when they are arranged in contact with each other. Also, a heat radiation plate having an area about ten times as large as the above sum of their cross sections and fins each having an area about 5 to 7 times as large as the above sum are provided to give a total radiation area about 100 to 200 times as large as the above sum. The heat radiation plate and fins are forcibly air-cooled by a fan or water cooled.
However, there is a strong demand to cool a large refrigeration panel to a low temperature without using a large radiation plate and forcible cooling. If such a demand is realized such devices will be widely used for the refrigeration panel of a large size and the wall of a cold reserving chamber.
Further, in a conventional structure, bedewings are apt to occur at the lower temperature side and disconnections are often caused at junctions between the element and the electrode by corrosion due to said bedewings.